Allow nav elements to be printed
Allow nav elements to be printed

Topic pages are essentially all `nav`, so when printed they currently
print just a blank page. Allow `nav` elements to be printed again.

https://trello.com/c/7GEsR48R/5-users-are-unable-to-print-topic-pages-me
dium

Example
https://www.gov.uk/land-registration/practice-guides

robinwhittleton/static,alphagov/static,tadast/static,kalleth/static,tadast/static,robinwhittleton/static,tadast/static,kalleth/static,alphagov/static,tadast/static,robinwhittleton/static,alphagov/static,kalleth/static,kalleth/static,robinwhittleton/static